Overview

The following study describes extending YANG language statements to allow customization of models.

YANG Language

The YANG language provides us the ability to define and model configurations and state data by defining YANG modules
- Modules contain a sequence of statements
  - Statement syntax is either of the following :
    - statement = keyword [argument] ;
    - statement = keyword [argument] { <substatement(s)..> } ;

* argument can be zero or one depending on the statement

* argument is a string

An XML-based equivalent version of YANG is called YIN
YANG uses a tree to define the hierarchy of data wherein each ‘node’ has a value or/and a set of child nodes
- 4 types of nodes
  - leaf nodes
  - container nodes
  - leaf-list nodes
  - list nodes

Figure 1.1 Schema tree of module 'stores'

stores module schema tree

YANG extension Statement

** the YIN version and Schema trees above are generated by YANG validator 'pyang'

Expected tree diagram for example-module based on RFC8340 (https://datatracker.ietf.org/doc/html/rfc8340):

Gliffy Diagram

macroId	c27dcf5f-85dc-4861-a7db-ff726ab42e91
displayName	Diagram 6
name	Diagram 6
pagePin	2

Existing YANG parser

(Please see https://wiki.onap.org/display/DW/Existing+Yang+Parser)

OpenDayLight Yang tools recognises YANG extensions

Contains interface which has methods to access data of a YANG extension statement

package org.opendaylight.yangtools.yang.model.api;
import org.opendaylight.yangtools.yang.model.api.stmt.ExtensionEffectiveStatement;
public interface ExtensionDefinition extends SchemaNode, EffectiveStatementEquivalent<ExtensionEffectiveStatement> {
    String getArgument();
    boolean isYinElement();
}